(a) Field of the Invention
The present invention relates to novel catalyst compositions and a method for preparing same. More particularly, the present invention relates to novel catalyst compositions which are extremely useful catalysts for hydrodesulfurizing or hydrodenitrifying hydrocarbon distillates containing sulfur-containing hydrocarbon molecules or nitrogen-containing hydrocarbon molecules, such as kerosene-gas oil distillates, and are also suitable catalysts for hydrogenating or hydro-refining various hydrocarbons, for example, for hydrogenating aromatic hydrocarbons such as dimethylnaphthalenes.
The present invention further relates to an advantageous process for hydrodesulfurizing sulfur-containing hydrocarbons by using the catalyst compositions as above described, which produces hydrocarbons well free of sulfur from various sulfur-containing hydrocarbons, for example hydrocarbon distillates containing sulfur-containing hydrocarbon molecules, such as kerosene-gas oil distillates.
(b) Description of the Related Art
Recently worldwide environmental disruption has become a serious problem. In particular, combustion of fossil fuels, such as petroleums and coals, and combustion of sulfur-containing fuels generate respectively nitrogen oxides (NO.sub.x) and sulfur oxides (SO.sub.x), which when released into the atmosphere, make acidic rain or acidic fog, causing severe damage to the natural environment of forests, lakes and marshes. Also, SO.sub.x, NO.sub.x and the particulates (for example, the particulates of soot, dust and mist) released with combustion exhaust exert a baneful influence upon human bodies inhaling them. This requires measures to reduce the release of these pollutants including SO.sub.x, NO.sub.x and the particulates, as far as possible.
A common measure of reducing the SO.sub.x release is a treatment after combustion, i.e. flue gas desulfurization, but it is impractical for moving exhaust sources such as motorcars even if it becomes operable technically. It is therefore desirable to reduce the sulfur content in fuels so that the flue gas desulfurization becomes unnecessary.
On the other hand, NO.sub.x generate necessarily even from fuels well denitrified except for combustion without air, and the particulates occur in a large quantity depending on the kinds of fuels and the manners of combustion, thereby necessitating exhaust gas treatments for inhibiting their release into the atmosphere.
In the case of stationary exhaust sources, such as boilers, it has become possible to remove fairly well the atmospheric pollutants, such as SO.sub.x, NO.sub.x and the particulates, by flue gas desulfurization or denitrogenation. However, in the case of diesel engines of trucks or the like, which are moving exhaust sources of these pollutants and release exhaust containing large quantities of NO.sub.x and the particulates including soot, these pollutants are released as they are into atmosphere because the removal thereof from the exhaust is technically difficult. Diesel engines utilize gas oils or the like as fuels and release exhaust containing SO.sub.x in a considerably high concentration because of the present insufficient reduction of sulfur content in the fuels. The SO.sub.x contained in the exhaust are not only a cause of atmospheric pollution but also one of the major obstacles in removing the NO.sub.x contained in the same exhaust. Removal of NO.sub.x from the exhaust from diesel engines requires treating the exhaust with after-treatment apparatuses and dehydrogenation catalysts. During such an after-treatment, if the concentration of the coexisting SO.sub.x has not been reduced sufficiently, poisoning of the catalysts is accelerated considerably, thereby making it difficult to stably maintain the catalytic functions for a long term. That is, sufficient reduction of the sulfur content in diesel fuels, such as gas oils, is necessary also from the viewpoint of maintaining the catalytic functions.
In addition to the problems in the fuel fields, sulfur compounds or organic nitrogen compounds contained in hydrocarbons generally deteriorate the catalytic functions in many catalytic processes, such as catalytic cracking or catalytic reforming processes. This also causes a strong demand for the development of improved techniques for effective removal of the sulfur compounds and organic nitrogen compounds from material hydrocarbons, particularly a strong demand for improved hydrodesulfurization catalysts and processes.
There have been developed many techniques for hydrodesulfurizing sulfur-containing hydrocarbons. Among various catalysts proposed in the conventional techniques as active catalysts for hydrodesulfurizing gas oil distillates or the like, typical ones widely used are catalysts obtained by improving those comprising an alumina and Group VIA and VIII metals of the Periodic table supported on the alumina, such as CoO.MoO.sub.3 /Al.sub.2 O.sub.3, NiO.MoO.sub.3 /Al.sub.2 O.sub.3 and NiO.WO.sub.3 /Al.sub.2 O.sub.3. For the reasons as above described, these conventional hydrodesulfurization catalysts however require further improvement in their catalytic functions.
These conventional hydrodesulfurization catalysts have generally been prepared by an impregnation technique, wherein an alumina support prepared by calcining an alumina gel is impregnated with metal salts of Group VIA metals and Group VIII metals. However, by the impregnation technique, it is difficult to improve the catalytic functions by increasing the ratio of the supported active metal components, i.e. the supported effective components consisting of Group VIA and Group VIII metals, because of the difficulty in impregnating an increased quantity of the active metal components, and even if it is performed, the supported active metal components cohere easily to lower their dispersion, and the lowered dispersion results in an insufficient improvement of activity or, under certain circumstances, rather reduces the catalytic functions including activity.
An improved technique is proposed in Japanese Patent Application Kokoku Koho (publication) No. 3-12935, wherein the impregnation is carried out in the presence of additives, such as oxy acids (aliphatic oxy acids). Nevertheless, the improved technique employing an impregnation technique also causes the cohesion of the metal components supported in an increased quantity, and cannot improve the activity sufficiently.
Another known method employs a kneading technique, wherein catalysts are prepared by calcining a kneaded mixture of an alumina gel (hydrogel) and metal salts (aqueous solution). This method is superior to the impregnation technique because the kneading technique generally permits stable support of a high percentage of the active metal components and is easy to operate. However, there are reports of the lower activity of the catalysts obtained by the kneading technique as compared with that of the catalysts obtained by the impregnation technique [Industrial Chemistry Journal (Kogyo Kagaku Zasshi), volume 74, No. 3, pages 330-335 (1971)].
There are some attempts to develop newly-contrived methods of preparing catalysts by employing kneading techniques. For example, there have been proposed a method of adding a phosphorus component into the kneading materials (Japanese Patent Application Kokai Koho (Laid-open) No. 61-123444) and a method of combining kneading and impregnation (Japanese Patent Application Kokai Koho (Laid-open) Nos. 61-138537 and 51-24593). However, these methods require very complicated procedures, which causes an increase in the production cost.